The invention relates to plants according to the introductory clause of claim 1, to conveyors according to the introductory clause of claim 8 and to pallets according to the introductory clause of claim 10.
When processing or treating containers, more particularly when producing them, the same are conveyed to processing stations to perform the respective processing steps, are transferred to them, if necessary, are treated and are subsequently carried away. In order to be able to process the container in a cost saving way, the conveying stations and the processing stations have to be well-suited to each other so that a high through-put of containers can be achieved by simple means without any interference. It has been found that known plants for producing containers have been further developed by some minor improvements of individual processing stations only while the conveying concept remained unchanged over a long period of time.
The bond to a seemingly unimpeachable conveying concept can, in particular, clearly be recognised in the production of cold-pressed containers, such as aerosol cans or tubes. FIG. 1 shows schematically the principal construction of known plants for producing aluminium cans. The procedure of manufacture begins with a pressing step of a press 30. Immediately afterwards, cutting to size and, optionally, brushing of the raw containers or cans is done in a raw processing machinery 31. Subsequently, the cans are put onto mandrels of a chain conveyor 32 and are led through a cleaning station 33 including a washing device and a drying device. After cleaning, the interior of the cans is coated with a varnish in an inside varnishing device 34. To this end, each can has to be removed from its mandrel of the chain conveyor, has to be put into a supporting pan, and has then to be introduced into a sleeve-like rotatable holder. The inside varnish is discharged from a nozzle which is movable into the interior of the can, while the can is rotated. After that, each can has to be removed from the holder, has to be put into a furnace pan and has to be conveyed in it through a first furnace 35 before being put again onto a mandrel of another chain conveyor 32.
For carrying out the movements along the can's longitudinal axis necessary for inside varnishing, energy intensive pulses of pressurised air are used. These pressurised air pulses, the movements of the supporting pans and the motion of the conveying chain have to be synchronised exactly. The supporting pans, die sleeve-like holders and the furnace pans are adapted to the respective actual can diameter and have to be exchanged for the production of cans of another diameter, thus, leading to long periods of disuse.
In order to compensate for short differences in through-put of the inside varnishing processing station 34, 35 and of the cleaning station 33, a first storage chain 36 is provided which reduces or increases the number of mandrels to be conveyed, correspondingly reducing or increasing the number of returning mandrels. A second storage chain 37 is provided after the inside varnishing station 34, 35 and before an outside processing station 38. The outside processing station 38 comprises an undercoating device 39, a printing device 40 and an overlying varnish device 41. In all three devices 39-41, the cans are put onto a mandrel, are coated and are put onto the chain again to be carried through a drying furnace. When performing this, due to the necessary movements of the cans, substantially the same problems will arise as in inside varnishing.
After outside coating 38, a third storage chain 42 and subsequently a final shaping device 43 is provided, as, for example, for aerosol cans for forming the can's neck, as well as a packing machine 44.
Conveying by chain conveyors which comprise laterally projecting mandrels in predetermined distances for holding the cans is the conveying concept used in the entire production line. The cans are aligned one dimensionally in fixed distances one after one so as to be moved, in average, with the same speed. This substantially rigid can movement throughout the whole plant results in synchronising problems at the processing stations. In order to compensate for local conveying variations due to the operation or its interruption, mechanically expensive compensation or storage devices have to be provided. In addition, the period of dwell of the cans within a processing zone has to be determined substantially by the length of the chain within this zone, resulting in an extremely large chain length in the furnaces because of the long drying periods. Due to this chain conveyor concept, linear production lines rigidly constructed will result which need large workshops, and in which all processing stations have to be matched to each other. In addition, the expenditures for servicing the conveying chain and the energy loss of the furnaces are very high.